Pond Boss Forums POND CONSTRUCTION Renovating a Pond or Lake? impending dam disaster

I can only speak in general measurements as this problem was just found. Here goes: I just returned from a 2 week vacation to find my pond water level down about a foot. Have looked at the drain and no water is coming through it. I had noticed what I thought was a new spring about 100 yards below the dam about a month ago, but didn't put this together with the pond as it seemed too far away from the dam. Yesterday I walked below the dam and the ground for about 100 feet wide and 50 feet deep was soggy to the point I could stick a metal rod in about 36 inches and it came out with water dripping from it. I had an excavating contractor who was working on building my house( which, by the way is SUPPOSED to overlook my pond) and he feels there is a leak in the dam. He suggests either draining the pond and repairing the dam, or going on the downstream side of the dam, digging down several feet, making the trench about 10 feet wide, then compacting clay-chert soil and essentially building a new dam below the existing one. At the same time, widening the downstream side of the existing dam to get a better ratio. ( he says the dam was built with a 1:1 ratio on bout the water side and the other, and should be a 3:1 ratio. Anyone have opinions on this technique? He is a fine man, a very good excavator, but honestly is not really familiar with how to do this.

I need to add what history I can to this story. I have owned the pond for 3 years,and even through the drought 2 years ago when many ponds completely dried up, this pond only lost 5 inches. It is spring fed as well as a significant water shed. This drop in water has been happening as I look back, for about 2-3 months but we have not had rain since July. The drastic drop has only occurred in the last 2-3 weeks which makes me thing something major has happened. The water level t the dam (6 feet deep) is approximately 30-40 feet above the ground level below the dam where it is wet at least 3 feet down.

I will let the experts chime in on this but is seems to me you may be dealing with two issues at once:

That is if your pond is tied into ground water then as the ground water goes down your pond will go down. It's probably no coincidence this is occurring during a drought.

Secondly, the wetness below the dam signals a problem but it may not be as serious as you think being that far away from the dam. IMHO the contractors second option of draining, installing a core trench and widening the dike with less slope is spot on, but like I said I am no expert on pond building, just have some experience in the installation of four ponds on my property.

If you go the secondary core trench route be sure the soil is damp and packed in layers preferably with a sheepsfoot roller.

I wouldn't cut into the actual dam if I didn't have to.

Working on the back side of the dam has it's dangers. If it were to give way, the operator would be in harms way rather quickly if there still was substantial water in the pond.

Would a coffer dam be an option to work on the"wet side" of the dam without draining the pond?

That's why I would prefer the option of draining the pond first.

I'm not familiar with a "coffer dam" although I've heard of it.

from my understanding, pilings would be driven in the waterside bottom out about 40 feet from the dam in a U shape, then wooden beams slid down to create a barrier to prevent the water from coming in to this area. Sometimes it can be done with a soil "dam, then ultimately pumped out to remove the seep in water. I have sen them drain canals in Venice for repair this way, and I know many times in seaport areas this technique is used to isolate some feature to repair, docks, etc

Makes sense but a packed core trench may be less costly and more effective due to specialized equipment and lumber for the above. Wood eventually rots although perhaps by that time the soil is sufficiently compacted to prevent seepage.

Cecil, I think he was saying use the coffer dam to facilitate repairs, then remove it after repairs are completed.

We used a coffer dam to hold back the spring while the dam was finished. They are a very good pond building concept.

Oops my bad. Sometimes I read too fast!

THat is what I planned, possibly using a coffer dam instead of draining the whole pond. I am waiting til the first of the week to get an estimate on repairs, but I am thinking this is a rather expensive problem to solve.

Jimmy,

Is getting the original excavator out to fix the problem at no charge due to it being his work an option? Some excavators will stand by their work.

Oh no, Cecil, this dam was built 20 years ago, and my excavator had nothing to do with it.

I just was reading about a product called ESS 13 that is supposed to be much better than bentonite. Anyone have any knowledge with this? I guess my concern is since the leak has increased greatly in the last month or so that any material like this will be too little too late.

While a few people have tried such products, there seems to be no consensus on how to ensure that it works the first time. If I remember correctly, more people have had success digging out the bad area and correctly re-packing good clay in the area in 6" lifts.

Search ESS-13 on here and read the results to make a decision for yourself.

I have been trying to fix a leaky pond for 5 years. I paid a lot of money to dig out the back side of the dam down as deep as we could go and rebuilding it from the backside. While it may have helped some it was basically a waste of money.

This year I bit the proverbial bullet and drained a 2.14 acre pond that was 17 feet at the dam and raised the bottom 3 feet using clay mixed with bentonite in 6" lifts compacting each lift with a 12 ton sheepsfoot roller.

My pond is spring and watershed fed as well so it is taking a long time to fill up. I am quite sure that the bottom is now sealed correctly doing it this way. I do still have water going into the overflow from somewhere and leaving at 12 GPH but that is another subject.

Bottom line is I feel like I wasted a lot of money and time trying to fix the pond from the back because I didn't want to drain it. It didn't work and I wouldn't advise anyone else to do it now. I feel strongly that leaks should be addressed from the water side and if that involves draining and starting over you will probably come out ahead in the long run.

Best of luck.

my gut reaction is like mark's....drain and get the root of the problem first, you can get a fishery back pretty fast.

jimmyt,

I have seen leaks fixed by the core trench method you described if the leak was due to water leaking under the dam. This is almost always a new pond that was not properly cored when built. A pond that has held water for 20 years and suddenly starts leaking seems like something else. I would be looking for causes such as a leaking drain structure, dead or removed trees that were on or near the levee, etc. If you are in a historically rare drought it could also be that a spring that formally supplied water to your pond has dried up and possibly collapsed and is now draining water away from the pond. If that is the case you may need to see the pond bottom to find the problem. I have found no "one cure fits all" for leaks. They often take quite a bit of investigating from an experienced pond builder.

there are so many issues, I am inclined right now to just wait a few weeks or months to see what happens. Th one factor that I keep coming back to is that ultimately draining the pond and fixing it by dredging out the sludge built up and fixing the dam seems like the best long-term option. One thing the excavator said was that with the lake being only 7 feet deep on the wet side and 25 feet from the ground level to the top of the dam seems to indicate that that the pond has silted up a great deal.

If the dam can be safely breached without damaging anything downstream, several feet of muck might wash out with the water.

jimmyt - all can say is good luck... I lost much hair, heart, funds, and water when a pond I had built on a ridge in NE 'bama decided to join with an underlying abandoned coal mine trace. Kinda sortof can laugh and smile now, years later, 3 states away later... but not easy seeing such disappear. Again, good luck, and FWIW, I'm with the vote of draining and fixing.